PFAS treatment process for liquid effluent

This application is a National Stage of International Application No. PCT/IB2021/056503 filed Jul. 19, 2021, claiming priority based on International Application No. PCT/IB2020/000618 filed Jul. 21, 2020.

Perfluoroalkyls and polyfluoroalkyl substances (PFAS) are a family of more than 4700 man-made emerging compounds with a completely or partially fluorinated hydrophobic alkyl chain, the most known families of which are perfluorinated carboxylic acids (PFCAs) and perfluorinated sulfonic acids (PFSAs).

PFAS have been used in numerous industrial applications, such as firefighting foams, coating, textile stain guards, etc., since 1940s because of their surfactant properties. PFAS can be released into the environment via numerous pathways including air, soil, and water and they have been detected in water sources, soil and biological samples.

PFAS have become an issue as emerging organic contaminants for they can be widely found in both wastewater effluent and drinking water worldwide, and also for their stability in the environment, potential for bioaccumulation and their negative health outcomes.

Due to the growing concerns on the ecological and human health effects of PFAS, many countries established regulations and guide values in drinking water, sources and soil for these compounds for long chains PFAS.

In the same time, industrials tried finding some new alternatives to replace these long-chain compounds introducing short-chain PFAS, a group of chemicals that are more water soluble and hydrophilic but with low bioaccumulation potential and less acute toxicity. However, these compounds are small and often more persistent resulting in long term risk concern.

As a consequence, water resources are being contaminated by a large variety of PFAS compounds having different carbon-chain (C-Chain) length and also different functionalities, properties, treatability.

Existing removal treatments for treating resources for drinking water production, use adsorbent materials, ion exchange resins, reverse osmosis or nanofiltration. Other treatments such as oxidation and especially advanced oxidation processes can be used for resources and soil remediation.

The most effective treatment technologies for PFAS having different carbon-chain length appear to be nanofiltration (NF) and reverse osmosis (RO), however these treatments are costly for design and operation.

Various sorbents have been reported to be effective in the removal of PFAS. These sorbents include granular activated carbon (GAC), powdered activated carbon (PAC), superfine powdered activated carbon (SPAC), anion-exchange resin, biomaterials, molecularly imprinted polymers (MIP) and mineral materials. Some adsorbents such as modified clays and cyclodextrin polymers have also shown their efficiency for some PFAS. Particularly, these adsorption technologies have been found to offer better economic performance compared to other removal techniques such as NF or RO. However, since PFASs molecules have hydrophilic groups and hydrophobic and oleophobic carbon-fluorine chains, their sorption behavior and mechanisms are complicated. The emerging PFAS compounds having short chain length and being polar and hydrophilic, are the most difficult to be removed by conventional treatment well adapted for long chains PFAS (adsorption on activated carbon, exchange on resin . . . ). Only NF or RO membranes processes can remove all PFAS compounds up to smaller chain-length.

There is therefore a need for a treatment able to remove PFAS whatever the length of their carbon chain, and their hydrophobicity, in particular at low cost.

The present invention relates to a method for controlling removal of perfluoroalkyls and polyfluoroalkyl substances PFAS from a liquid effluent by means of a control system including a PFAS treatment unit dedicated to the treatment of PFAS including at least one treatment stage optionally chosen from a short and long chain PFAS dedicated treatment stage, a short chain PFAS dedicated treatment stage and a long chain PFAS dedicated treatment stage.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the presently disclosed subject matter. While the following terms are believed to be well understood by one of ordinary skill in the art, the following definitions are set forth to facilitate explanation of the presently disclosed subject matter.

All technical and scientific terms used herein, unless otherwise defined below, are intended to have the same meaning as commonly understood by one of ordinary skill in the art. References to techniques employed herein are intended to refer to the techniques as commonly understood in the art, including variations on those techniques or substitutions of equivalent techniques that would be apparent to one skilled in the art. In describing the presently disclosed subject matter, it will be understood that a number of techniques and steps are disclosed. Each of these has individual benefit and each can also be used in conjunction with one or more, or in some cases all, of the other disclosed techniques.

Perfluoroalkyl substances are fully fluorinated (perfluoro-) alkane (carbon-chain) molecules. Their basic chemical structure is a chain (or tail) of two or more carbon atoms with a charged functional group head attached at one end. The common functional groups are carboxylates or sulfonates, but other forms are also detected in the environment. Fluorine atoms are attached to all possible bonding sites along the carbon chain of the tail, except for one bonding site on the last carbon where the functional group head is attached. This structure can be written as CF—R, where “CF” defines the length of the perfluoroalkyl chain tail, “n” is >2, and “R” represents the attached functional group head. Note that the functional group may contain 1 or more carbon atoms, which are included in the total number of carbons when naming the compound.

Perfluoroalkyl acids (PFAAs) are some of the most basic PFAS molecules. They are essentially non-degradable and currently are the class of PFAS most commonly tested for in the environment. The PFAA class is divided into two major groups:

Perfluoroalkane sulfonamides (FASAs, CF—R, with R=—SONH), such as perfluorooctane sulfonamide (FOSA, CFSONH), are used as raw material to make perfluoroalkyl sulfonamide substances that are used for surfactants and surface treatments. FASAs can degrade to form PFAAs such as PFOS.

Polyfluoroalkyl substances are distinguished from perfluoroalkyl substances by not being fully fluorinated. Instead, they have a non-fluorine atom (typically hydrogen or oxygen) attached to at least one, but not all, carbon atoms, while at least two or more of the remaining carbon atoms in the carbon chain tail are fully fluorinated. The carbon-hydrogen (or other non-fluorinated) bond in polyfluoroalkyl molecules creates a “weak” point in the carbon chain that is susceptible to biotic or abiotic degradation.

As a result, many polyfluoroalkyl substances that contain a perfluoroalkyl CFgroup are potential precursor compounds that have the potential to be transformed into PFAAs.

Long-chain refers commonly to:

Short-chain refers commonly to:

Liquid effluent in the meaning of said invention includes raw water, urban effluents, industrial effluents.

Raw water in the meaning of said invention includes any water intended for drinking water production, such as ground water or resources water, as well as surface water.

Urban effluents include wastewater, leachates, effluents from waste truck wash. Urban wastewater includes domestic wastewater coming from households, municipal wastewater issued from public facilities, commercial and institutional facilities, and eventually industrial wastewater (by-product of industrial or commercial activities).

Industrial effluents include liquid waste or sewage discharged by industrial activities, including leachates. Leachates are the result of water percolating through domestic, agricultural or industrial waste stored in a landfill.

In the meaning of said invention, a short chain PFAS dedicated treatment stage is a treatment stage able to treat, i.e. to remove, short chain PFAS. A long chain PFAS dedicated treatment stage is a treatment stage able to treat, i.e. to remove, long chain PFAS. Similarly, a short and long chain PFAS dedicated treatment stage is a treatment stage able to treat, i.e. to remove, both short and long chain PFAS either by combination of a short chain PFAS dedicated treatment stage and a long chain PFAS dedicated treatment stage, for example by mixture of reagents, each reagent being dedicated to remove short or long chain PFAs, or by an appropriate treatment able to treat both short and long chain PFAS.

In particular, a short and/or long chain PFAS dedicated treatment stage can be defined as a treatment stage having a short and/or long chain PFAS removal efficiency sufficient to attain a pre-defined final concentration of short and/or long chain PFAS at its outlet in an effluent having a given initial concentration in short and/or long chain PFAS. This pre-defined final concentration is for example imposed by regulation or a user.

This removal efficiency is typically of at least 70%, preferably of at least 80%, most preferably of at least 90% but could be different depending on the initial concentration of PFAS and the targeted final concentration.

“Removal efficiency” or “efficiency of the removal” or “m % removal” is defined by the formula (1):Removal efficiency (%)=[1−()]·100  (1)

Where x is the mass content of PFAS before treatment and y is the mass content of PFAS after treatment. This mass content of PFAS may be measured by liquid chromatography coupled with mass spectroscopy (standard methods EPA 533 and 537.1 and standard ISO 21675:2019)

According to a first aspect, a method for controlling PFAS removal from a liquid effluent by means of a control system is provided, said control system including a PFAS treatment unit dedicated to the removal of perfluoroalkyls and polyfluoroalkyl substances PFAS. The PFAS treatment unit includes at least one treatment stage optionally chosen from a short and long chain PFAS dedicated treatment stage, a short chain PFAS dedicated treatment stage and a long chain PFAS dedicated treatment stage.

The method comprises:

The method of the invention thus allows activating the PFAS treatment unit only when necessary, which allows reducing the maintenance of the PFAS unit, and the operating costs. Such activation occurs only when information representative of the presence of PFAS is provided.

Advantageously, the method may comprise a further step (D) of activating said at least one treatment stage of the PFAS treatment unit, in particular in response to said transmitted at least one activating signal, optionally activating the corresponding at least one PFAS treatment stage chosen from a short and long chain PFAS dedicated treatment stage, a short chain PFAS dedicated treatment stage and a long chain PFAS dedicated treatment stage, removing thereby at least a part of the PFAS from the liquid effluent.

In particular, the PFAS treatment unit may include one or more PFAS treatment stage, able to treat both short and long chain PFAS, short chain PFAS and long chain PFAS. In such a case, the activating signal activates said corresponding PFAS treatment stage of the PFAS treatment unit. Each treatment stage is then activated only when necessary. It should be noted that several activating signals can be generated for activating several PFAS dedicated treatment stages to achieve a specific removal efficiency.

The liquid effluent to treat by the control system of the present invention may be selected from raw water, urban effluents, industrial effluents and two or more of these effluents. Such effluent contains more than 50 vol % of water, in general more than 60 vol % of water. In some embodiments, the water content may be at least of 95 vol %, or even at least of 99 vol %, for example up to 99.9 vol %, or even up to 100 vol %. The water content may be within any range defined by the previously cited limits. In general, the remaining percents are solids, such as particles, suspended matter, colloids, etc.

Advantageously, the PFAS treatment unit may comprise at least one treatment stage chosen from a short chain PFAS dedicated treatment stage and a long chain PFAS dedicated treatment stage, such that the treatment stage specific to short/long chain PFAS can be activated, in particular when the provided information data include information data representative of the chemical formula of at least one PFAS which is a short/long chain PFAS. In such a case, a better removal of the PFAS can be achieved as the treatment stage is dedicated to the removal of the particular short/long chain PFAS. This allows to attain a national regulation requirement for the content of PFAS in liquid effluent in a more efficient and sure way, in particular when the considered PFAS are present at a very low level in the liquid effluent. Such specific treatment stages may require costly systems or reagents such that the process of the invention allows further cost reduction. Moreover, it is possible to choose to activate one or the other PFAS treatment stage depending on the PFAS present in the liquid effluent. As it is expected that the content of liquid effluent in short chain PFAS will increase to the detriment of long chain PFAS, the method of the invention allows easy and efficient adaptation of the PFAS removal treatment to the liquid effluent. Finally, the control system for PFAS removal of the present invention is preferably intended to be integrated into a liquid effluent treatment facility. In such a case, it is possible to change the nature of the PFAS treatment unit or its reagent to be more effective to remove PFAS identified in the liquid effluent to treat, without stopping the whole liquid effluent treatment.

It should be noted that at least one of the treatment stage may be a short and long chain dedicated treatment stage which could be used in combination with the above mentioned short chain dedicated treatment stage and/or long chain dedicated treatment stage, for example for treating a part of the liquid effluent, the remaining of the effluent being treated by one or several of other treatment stages of the PFAS treatment unit.

The information data provided in step (A) may be information data related to targeted PFAS, for example PFAS of a registered list of targeted PFAS, this list including the chemical formulas of targeted short chain PFAS, targeted long chain PFAS, or both. Such a list may correspond to a list of PFAS provided in a national regulation, for example the US regulation or the coming EP regulation, or provided by any other institution or company, or by plant operator as a targeted list of PFAS to be specially controlled and treated.

Advantageously, step (A) for providing information data may include:

Most of these information data are non specific to a particular PFAS, in the sense that they do not allow an accurate identification of the PFAS, and only provide an information of presence/absence of PFAS to allow activation of the PFAS treatment unit when PFAS are detected, whatever the nature of the PFAS.

By this way, several kinds of information data may be used to generate an activation signal in step (B). Information data such as data representative of the presence of carbon-fluorine bonds, data representative of the presence of fluorine, data representative of the chemical formula and data representative of an estimated total concentration of targeted PFAS may be performed by non targeted analysis of the liquid effluent, although targeted analysis is possible. By non targeted analysis, we mean an analysis which provides information on all the fluorinated compounds potentially present in the liquid effluent, in opposition to a targeted analysis which provides information on one or several specific fluorinated compounds. In other words, the targeted analysis is an analysis providing information data that can be attributed to a specific targeted PFAS of known structure, i.e. structurally identified. A targeted analysis thus allows searching and quantifying one or several specific PFAS. Such targeted analysis may be adapted to the analysis of a single specific targeted PFAS or may be adapted to the analysis of a group of specific targeted PFAS. On the contrary, a non targeted analysis is an analysis providing information data relative to a group of PFAS (which may be part of a registered list of PFAS or not), and provides information data that can only be attributed to this group of PFAS, without possibility to attribute the data to any specific PFAS contained in the group. Thus, in general, non targeted analysis does not allow to provide concentration data, or with a low accuracy, and do not allow to provide the exact structure of the compounds analyzed. On the contrary, targeted analysis is performed on one or several compounds structurally defined and provides an accurate measure of the concentration of the analyzed compounds.

The determination of the above information data may include, or consist of:

The pre-defined threshold may be fixed by regulation or user.

Registered data obtained from a targeted analysis may be data representative of the concentration of at least one PFAS. Registered data obtained from a non targeted analysis may be data representative of the presence of carbon-fluorine bonds, data representative of the presence of fluorine or data representative of the chemical formula.

The extracted information data may be a PFAS specific signal intensity, a PFAS specific signal surface, a sum of the intensities of a group of PFAS specific signals, a sum of the surfaces of a group of PFAS specific signals, a sum of the intensities of all PFAS specific signals.

The PFAS specific signal(s) and/or the pre-defined threshold and/or the predefined range may be determined by performing the same targeted or non-targeted analysis on effluents having different known concentrations of PFAS, in particular of PFAS of a registered list. This determination may result from a statistical analysis of the data registered by the targeted or non targeted analysis or from an analysis or comparison with data previously obtained from known effluents.

In one embodiment, the determination of the above information data may include, or consist of:

The PFAS total concentration data may be estimated using a correlation previously established which correlates the extracted information data with a PFAS total concentration. This embodiment is particularly adapted to high resolution mass spectroscopy non targeted analysis.

It may be advantageous to be able to more specifically conduct the PFAS removal. Thus, in a preferred embodiment, step (A) for providing information data may include: